diff --git a/otouto/plugins/media.lua b/otouto/plugins/media.lua
index bd1ba4a..f566995 100644
--- a/otouto/plugins/media.lua
+++ b/otouto/plugins/media.lua
@@ -1,5 +1,8 @@
 local media = {}
 
+local HTTP = require('socket.http')
+local HTTPS = require('ssl.https')
+local redis = (loadfile "./otouto/redis.lua")()
 local utilities = require('otouto.utilities')
 local mimetype = (loadfile "./otouto/mimetype.lua")()
 
@@ -26,42 +29,91 @@ media.triggers = {
 function media:action(msg)
   local url = matches[1]
   local ext = matches[2]
+  local hash = 'telegram:cache:sent_file'
+  local cached_file_id = redis:hget(hash..':'..url, 'file_id')
+  local cached_last_modified = redis:hget(hash..':'..url, 'last_modified')
   local receiver = msg.chat.id
+  
+  -- Last-Modified-Header auslesen
+  local doer = HTTP
+  local do_redir = true
+  if url:match('^https') then
+	doer = HTTPS
+	do_redir = false
+  end
+  local _, c, h = doer.request {
+	method = "HEAD",
+	url = url,
+	redirect = do_redir
+  }
+  
+  if c ~= 200 then
+    if cached_file_id then
+      redis:del(hash..':'..url)
+	end
+    return
+  end
 
   utilities.send_typing(self, receiver, 'upload_document')
-  local file = download_to_file(url)
+  if not h["last-modified"] and not h["Last-Modified"] then
+	nocache = true
+	last_modified = nil
+  else
+    nocache = false
+	last_modified = h["last-modified"]
+	if not last_modified then
+	  last_modified = h["Last-Modified"]
+	end
+  end
+
   local mime_type = mimetype.get_content_type_no_sub(ext)
+  
+  if not nocache then
+    if last_modified == cached_last_modified then
+      print('File not modified and already cached')
+      nocache = true
+	  file = cached_file_id
+    else
+	  print('File cached, but modified or not already cached. (Re)downloading...')
+      file = download_to_file(url)
+    end
+  else
+    print('No Last-Modified header!')
+    file = download_to_file(url)
+  end
 
   if ext == 'gif' then
     print('send gif')
-    utilities.send_document(self, receiver, file, nil, msg.message_id)
-	return
-
-  elseif mime_type == 'text' then
-    print('send_document')
-    utilities.send_document(self, receiver, file, nil, msg.message_id)
-	return
-  
-  elseif mime_type == 'image' then
-    print('send_photo')
-    utilities.send_photo(self, receiver, file, nil, msg.message_id)
-	return
-  
+    result = utilities.send_document(self, receiver, file, nil, msg.message_id)
   elseif mime_type == 'audio' then
     print('send_audio')
-    utilities.send_audio(self, receiver, file, nil, msg.message_id)
-	return
-
+    result = utilities.send_audio(self, receiver, file, nil, msg.message_id)
   elseif mime_type == 'video' then
     print('send_video')
-	utilities.send_video(self, receiver, file, nil, msg.message_id)
-	return
-  
+	result = utilities.send_video(self, receiver, file, nil, msg.message_id)
   else
     print('send_file')
-    utilities.send_document(self, receiver, file, nil, msg.message_id)
-	return
+    result = utilities.send_document(self, receiver, file, nil, msg.message_id)
   end
+  
+  if nocache then return end
+  if not result then return end
+
+  -- Cache File-ID und Last-Modified-Header in Redis
+  if result.result.video then
+    file_id = result.result.video.file_id
+  elseif result.result.audio then
+    file_id = result.result.audio.file_id
+  elseif result.result.voice then
+    file_id = result.result.voice.file_id
+  else
+    file_id = result.result.document.file_id
+  end
+  redis:hset(hash..':'..url, 'file_id', file_id)
+  redis:hset(hash..':'..url, 'last_modified', last_modified)
+  -- Why do we set a TTL? Because Telegram recycles outgoing file_id's
+  -- See: https://core.telegram.org/bots/faq#can-i-count-on-file-ids-to-be-persistent
+  redis:expire(hash..':'..url, 5259600) -- 2 months
 end
 
 return media